Canning or otherwise packaging foods to preserve and store them for long periods of time has been an important part of food processing since the eighteenth century, when a Parisian chef named Appert devised a crude method of canning. Appert's process was introduced into the United States through England in about 1818. Canning remained an inexact process until Louis Pasteur applied his principles of fermentation to it in 1895.
Today, from picking to packaging, canning is a highly-developed, scientific industry. Foodstuffs are packaged in many different types of containers, with metal cans, glass jars and plastic packages being used on a wide scale. For convenience, the packaging of foodstuffs in rigid containers (i.e., cans, jars and rigid plastic packages) will be referred to collectively herein as "canning." No matter what type of container is used, however, all canning processes must deal with the sensitivity of most foods to oxygen. As anyone who has sliced a fresh apple knows, oxygen in the air immediately begins to react with fresh foods and leads to the loss of their organoleptic qualities and to their rapid spoilage. All foods are sensitive to oxygen in varying degrees, and the successful preservation of foods by canning requires, as an important step, the elimination of oxygen and other gases from the containers.
However, the containers themselves may be difficult to open after processing, because of the high degree of vacuum inside them. In particular, when the containers are screw-top jars, consumers often have great difficulty in unscrewing the caps. Moreover, this problem is not unique to the disclosed process, but occurs in other vacuum packaging processes as well. This problem has led to a proliferation of tools, devices, and "gadgets" to open tightly sealed screw-on caps. Thus, there is a need for a cap, in particular but not necessarily a screw-on cap, which maintains a hermetic seal to maintain a high vacuum, but which can be opened easily, without the need for special tools.